Question

Сколько дров надо сжечь в печке с КПД 40%, чтобы получить из 200 килограмм снега, взятого при температуре -10 градусов цельсия, воду при температуре 20 градусов цельсия.Ответ 18 килограммов. Нужно решение.

Answer 1

Дрова горят- энергия выделяется, причем только 40% идет на то, чтобы лед грелся от -10 до 0, затем плавится, полученная вода нагревалась от 0 до 20

Ну, а теперь формулами

$\eta Q(sg)=Q(nl)+Q(pl)+Q(nv)$

$\eta Q (sg)=\eta*m(d)q$

$\eta =0.4$

теплота сгорания дров

$Q (sg)=m(d)q$

теплота нагревания льда

$Q(nl)=c(l)m*(0-(-10)=2100*200*10=42*10 ^{5} Dg$

теплота плавления

$Q(pl)=\lambda m=340*10 ^{3} *200=680*10 ^{5} Dg$

теплота нагревания воды

$Q(nv)=c(v)m(20-0)=4200*200*20=168*10 ^{5} Dg$

сложим

$Q(nl)+Q(pl)+Q(nv)=42+680+168=89*10^{6}Dg$

подставим

$\eta Q (sg)=\eta m(d)q =Q(nl)+Q(pl)+Q(nv)=89*10^{6}Dg$

удельная теплота сгорания $q=12.4kDg/kg$ значение табличное, причем изменяется от 12 до 17 кДж/кг, в зависимости от вида дров

выражаем

$m= \frac{89*10^{6}}{\eta q} = \frac{89*10^{6}}{0.4*12.4*10 ^{6} } =17.94 kg$ приблизительно 18 кг Ответ

Answer 2

Calculation of the Amount of Wood Required to Heat Snow to Water

To calculate the amount of wood required to heat 200 kilograms of snow at -10 degrees Celsius to water at 20 degrees Celsius, we need to consider the efficiency of the stove. The given efficiency of the stove is 40%.

The formula to calculate the amount of heat required is:

Q = m * c * ΔT

Where: - Q is the amount of heat required - m is the mass of the substance (in this case, snow) - c is the specific heat capacity of the substance - ΔT is the change in temperature

First, let's calculate the amount of heat required to heat the snow to water:

Q1 = m * c1 * ΔT1

Where: - m = 200 kg (mass of snow) - c1 = specific heat capacity of snow (assumed to be 2.09 J/g°C)- ΔT1 = change in temperature = 20°C - (-10°C) = 30°C

Q1 = 200 kg * 2.09 J/g°C * 30°C = 12540 kJ

Next, let's calculate the amount of heat produced by burning wood in the stove:

Q2 = Q1 / η

Where: - η = efficiency of the stove = 40% = 0.4

Q2 = 12540 kJ / 0.4 = 31350 kJ

Now, let's calculate the amount of wood required to produce this amount of heat:

Q2 = m2 * c2 * ΔT2

Where: - m2 = mass of wood - c2 = specific heat capacity of wood (assumed to be 2.2 J/g°C)- ΔT2 = change in temperature = 31350 kJ / (m2 * c2)

To find the mass of wood required, we need to know the specific heat capacity of wood. Unfortunately, the specific heat capacity of wood can vary depending on the type of wood and its moisture content. Without this specific information, it is not possible to calculate the exact amount of wood required.

Therefore, we cannot provide an accurate answer to the question of how many kilograms of wood are needed to heat the snow to water. The calculation requires the specific heat capacity of wood, which is not provided in the question.

Please note that the specific heat capacity of wood can vary between 1.67 J/g°C and 2.5 J/g°C, depending on the type of wood and its moisture content